The present invention relates, in general, to power conversion and, more specifically, to a bi-directional AC/DC converter and a method of operation of the converter.
Applicants are unfamiliar with any AC/DC power supply converter that provide the following characteristics:
1. Provide galvanic isolation between input and output sides of the converter unit;
2. Be able to work with an active load (a load that can sink or source energy, such as battery, for instance), by sourcing energy into the load or sinking energy generated by the load;
3. Recycle energy when working with an active load by returning the energy into the electrical main of the unit; and
4. Provide Power Factor Correction for the line current, regardless if the energy is taken from the mains or recycled into the mains.
Different variations of isolated converters that provide Power Factor Correction have been described in Hirachi et al""s article entitled Switched-Mode PFC Rectifier with High Frequency Transformer Link for High-Power Density Single Phase UPS, Proceedings of the PESC Conference, June 1997, p. 290-96; Cho et al.""s article entitled Zero-Voltage-Transition Isolated PWM Boost Converter for Single Stage Power Factor Correction, Proceedings of the APEC conference, March 1997, p. 471-76; and Dalal""s article 400 W Single-Stage Current-Fed Isolated Boost Converter with PFC, Unitrode Power Supply Seminar 1999-00 Series, Manual SLUP002, p. 3.1-3.24. These articles disclose a process to integrate a Power Factor Correction circuit with a DC/DC converter stage to obtain circuits simpler than classic, two-stage approaches (a PFC regulator and DC/DC converter as a separate, basically independent units).
In particular, the Hirachi et al. reference presents an isolated AC/DC/AC converter for use in uninterruptible power systems. Comparison between conventional circuit configurations, which are based on non-isolated boost topologies and proposed solutions, which is basically an isolated boost converter, with a diode bridge and a separate MOSFET bridge on the primary side and a rectifier bridge on the secondary side.
Cho et al. disclose an isolated boost converter consisting of a diode rectifier bridge and a MOSFET bridge on the primary side and a diode bridge of the secondary side with additional circuitry located also on the secondary side, for minimizing switching loss in the AC/DC converter.
Dalal suggest a current fed isolated AC/DC converter topology based on the push-pull converter and typically consisting of a bridge rectifier on the input, center-tapped transformer and two MOSFET switches on the primary side and a diode rectifier bridge on the secondary side of the unit.
However, these articles do not disclose a system that can (1) be able to work with an active load (a load that can sink or source energy, such as battery, for instance), by sourcing energy into the load or sinking energy generated by the load; (2) recycle energy when working with an active load by returning it into the mains; or (3) provide Power Factor Correction for the line current, regardless if the energy is taken from the mains or recycled into the mains.
Furthermore, several solutions for non-isolated topologies (Wang et al. in the article entitled Some Novel Four-Quadrant DCxe2x80x94DC Converters, Proceeding of the PESC Conference, June 1998, p. 1775-82;) and an isolated topologies (Reimann et al.""s article entitled A Novel Control Principle of Bi-Directional DCxe2x80x94Dc Power Conversion, Proceedings of the PESC Conference, June 1997, p. 978-84; and Huang et al.""s article entitled Novel Current Mode Bi-directional High-Frequency Link DC/AC Converter for UPS, Proceedings of the PESC Conference, June 1998, p. 1867-71) capable of transferring energy from the DC source to the DC or AC load and also in the opposite direction (bi-directional power flow) have been presented. The topologies disclosed in those article do not disclose systems capable of (1) recycling energy when working with an active load by returning it into the mains; or (2) providing Power Factor Correction for the line current, regardless if the energy is taken from the mains or recycled into the mains. Moreover, the Wang et al. reference fails to disclose a method for providing galvanic isolation between input and output sides of the unit.
In particular, Wang et al. disclose a family of four topologies capable of operating in all four quadrants. This is a family of non-isolated converters, operating from a DC source and capable of generating both positive and negative polarity of output voltages, in addition to positive and negative output current, as may be directed by the load.
Reimann et al. suggest an isolated DC/DC converter topology capable of controlling energy flow in both directionsxe2x80x94from source to load and from load side to the source side of the unit. It is basically an isolated boost topology consisting of two bridges, one on the primary side and the other on the secondary side, each having four quasi-bidirectional switches.
Also, there are products on the market (such as BOP series from KEPCO, Inc.) which are capable of controlling active loads. These products, made by the applicant, lack the ability to (1) recycle energy when working with an active load by returning it into the mains; or (2) provide Power Factor Correction for the line current, regardless if the energy is taken from the mains or recycled into the mains.
Work described in Hui et al.""s article entitled A Bi-Directional AC-DC Power Converter with Power Factor Correction (Proceedings of the PESC Conference, June 1998, p. 1323-29) presents a non-isolated topology providing a bidirectional link between AC line and DC source capable of recycling the energy, but it does not provide galvanic isolation between input and output.
As in inventor""s knowledge, there has not been unit presented so far that can simultaneously satisfy the following requirements: (1) providing galvanic isolation between input and output sides of the converter unit; (2) be able to work with an active load (a load that can sink or source energy, such as battery, for instance), by sourcing energy into the load or sinking energy generated by the load; (3) recycle energy when working with an active load by returning the energy into the electrical main of the unit; and (4) provide Power Factor Correction for the line current, regardless if the energy is taken from the mains or recycled into the mains.
An isolated, bidirectional AC/DC converter with Power Factor Correction function and capability to recuperate energy into the mains has been invented. It consists of a power stage and a control section. The power stage processes raw power from electrical mains to the power required by the load. The power stage also processes the power generated by an active load and delivers the energy to the mains during the recuperation phase. The power stage has an input filter inductor, at least four bidirectional switches that form a bridge configuration on the primary side of an isolation transformer, the isolation transformer, at least four quasi-bidirectional switches that form a bridge on the secondary side of the isolation transformer and an output filter capacitor.
The control section of the unit regulates the current on the primary side and voltage on the secondary side. The function of the control circuit is to satisfy load requirements and provide Power Factor Correction. The control section has two distinctive parts. The first part controls the unit when the power is being delivered to the load (sourcing). The second part controls the unit when an active load is present and the power gets recycled into the mains (recuperation). Each art of the control section is in control only when needed, which is ensured by utilizing a circuitry that automatically disables itself when conditions for each part to take over are met.
The present invention is capable of satisfying all four requirements of (1) providing galvanic isolation between input and output sides of the converter unit; (2) be able to work with an active load (a load that can sink or source energy, such as battery, for instance), by sourcing energy into the load or sinking energy generated by the load; (3) recycle energy when working with an active load by returning the energy into the electrical main of the unit; and (4) provide Power Factor Correction for the line current, regardless if the energy is taken from the mains or recycled into the mains. The output voltage in the present invention effectively has two levels, one during sourcing, and the other, slightly higher one, during recuperation.